As is known, helicopters normally comprise a number of transmissions for transmitting motion from one or more turbines to the main rotor and/or tail rotor, and/or from the turbine to a number of accessory devices, i.e. for supplying energy, for example, by which to power the on-board equipment.
More specifically, transmissions are known comprising a number of gears, which mesh with one another by means of respective teeth to transmit a desired power value.
In known manner, the teeth of each gear have an involute profile to optimize power transmission and reduce the noise level of the transmission.
In operating conditions, the profiles of the meshing teeth on the gears deviate from the theoretical involute configuration, on account of the geometric and dimensional tolerances and deformation under stress of the teeth.
As a result, the actual position of the meshing teeth deviates from the theoretical position the teeth would have if they had no geometric or dimensional tolerances, and if the profile were undeformed under stress.
Which deviation is due to the elasticity and configuration of the profile of the teeth meshing at the time, and therefore varies during operation of the gears, even with no change in the power transmitted by the gears.
Such deviations produce noise and vibration which, as observed by the Applicant, are not uniform alongside variations in the power transmitted by the gears.